The present application relates to a GaN-based semiconductor light-emitting element, a light-emitting element assembly and a light-emitting apparatus each having such a GaN-based semiconductor light-emitting element, a method of manufacturing such a GaN-based semiconductor light-emitting element according to an embodiment, a method of driving such a GaN-based semiconductor light-emitting element, and an image display apparatus having such a GaN-based semiconductor light-emitting element.
In a light-emitting element (GaN-based semiconductor light-emitting element) having an active layer composed of a gallium nitride (GaN)-based compound semiconductor, the band-gap energy can be controlled by changing the compound crystal composition or thickness of the active layer, and thus it is possible to realize a light emission wavelength in a wide range from ultraviolet to infrared. GaN-based semiconductor light-emitting elements emitting light of various colors have already been commercially available and used in a variety of applications, such as image display apparatuses, illumination apparatuses, testing apparatuses, and sterilizing light sources. Furthermore, blue-violet semiconductor lasers and light-emitting diodes (LEDs) have also been developed and used as writing/reading pickups of large-capacity optical disks.
In general, a GaN-based semiconductor light-emitting element has a structure in which a first GaN-based compound semiconductor layer of n-conductivity type, an active layer, and a second GaN-based compound semiconductor layer of p-conductivity type are sequentially stacked.
In the related art, for example, a second GaN-based compound semiconductor layer having a superlattice structure including a Mg-doped AlGaN layer and a Mg-doped GaN layer is formed above an active layer, the superlattice structure being subjected to uniform doping or modulation doping. Formation of such a second GaN-based compound semiconductor layer having a superlattice structure has been reported to have an effect of increasing the hole concentration (for example, refer to K. Kumakura and N. Kobayashi, Jpn. J. Appl. Phys. vol. 38 (1999) pp. L1012; P. Kozodoy et al., Appl. Phys. Lett. 75, 2444 (1999); and P. Kozodoy et al., Appl. Phys. Lett. 74, 3681 (1999)). In this technique, high hole concentrations are obtained two-dimensionally by the piezoelectric effect due to strain, and it has been reported that by optimizing the period of the superlattice structure, the same effect (i.e., decrease in series resistance) can also be obtained with respect to the conduction in the thickness direction of the second GaN-based compound semiconductor layer.